It is ordinarily known to use a polymer compound having an ethylenically unsaturated double bond in a polymerizable composition in order to increase a crosslinking property. The increase in crosslinking density of the polymerizable composition is the most important technique in the field of using polymerizable composition.
For instance, in the case of using the polymerizable composition in the use requiring development processing, for example, with an aqueous solution or in the use where hydrophilicity of a cured film functions, it is needed to introduce a hydrophilic component into the polymerizable composition, and it is necessary for the polymerized cured film to have a high crosslinking density in order to fulfill requirement, for example, durability in water or nonswellability.
An example of material using such a polymerizable composition includes a lithographic printing plate precursor.
The lithographic printing plate precursor comprises an oleophilic image-recording layer provided on a hydrophilic support and is used to obtain a lithographic printing plate by a process including imagewise exposure with laser and then development processing, for example, with an alkaline developer to remove the unnecessary image-recording layer corresponding to the non-image area by dissolving while leaving the image-recording layer corresponding to the image area.
In view of response to a global environmental problem, simplification or elimination of the development processing has been pursued. As one method for simplification of the development processing, a method referred to as an “on-press development” is practiced. Specifically, according to the method after exposure of a lithographic printing plate precursor, the lithographic printing plate precursor is mounted as it is on a printing machine without conducting conventional development processing and removal of the unnecessary area of image-recording layer is performed with dampening water and/or ink at an early stage of printing step. Also, as a method of simple development, a method referred to as a “gum development” is practiced wherein the removal of the unnecessary area of image-recording layer is performed using not a conventional highly alkaline developer but a finisher or gum solution having pH close to neutral.
In the simplification of plate making operation as described above, a system using a lithographic printing plate precursor capable of being handled in a bright room or under a yellow lump and a light source is preferred from the standpoint of workability. Thus, as the light source, a semiconductor laser emitting an infrared ray having a wavelength of 760 to 1,200 or a solid laser, for example, YAG laser, is used. An UV laser can also be used.
As the lithographic printing plate precursor capable of undergoing on-press development, for instance, a lithographic printing plate precursor having provided on a support, an image-recording layer (photosensitive layer) containing an infrared absorbing agent, a radical polymerization initiator and a polymerizable compound is described in JP-A-2002-287334 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). Also, as the lithographic printing plate precursor capable of undergoing gum development, for instance, a lithographic printing plate precursor wherein the development is conducted with a finisher or a gum solution having pH close to neutral is known as described in EP-A-1751625 or EP-A-1868036.
In such a lithographic printing plate precursor of a simple processing type, an image-recording layer having a high hydrophilicity is used in order to make possible development with a developer having pH close to neutral or dampening water on a printing machine and as a result, strength of the image area becomes weak with dampening water during printing to cause a problem in that sufficient printing durability can not be obtained.
In view of the above problems, in JP-A-2006-111860 or JP-A-2009-29124, a lithographic printing plate precursor capable of undergoing on-press development having an image-recording layer comprising a laser-sensitive polymerizable composition containing a polymer compound having a radical polymerizable group is proposed. However, the radical polymerizable group described in JP-A-2006-111860 or JP-A-2009-29124 does not achieve sufficient printing durability. Further, the polymer compound is still insufficient in the developing property in the simple processing.